Make the Registry send a REGISTER_RESPONSE back to the messaging node

[notskm]

The REGISTER_RESPONSE contains the following information:
Message Type (int): REGISTER_RESPONSE
Status Code (byte): SUCCESS or FAILURE
Additional Info (String):

On success:

• Additional info includes the number of entries in the registry
• “Registration request successful. The number of messaging nodes currently constituting the overlay is (5)”

On failure:

• Additional info includes a reason for the failure

On communication failure:

• Remove the messaging node from the registry